1. Field of the Invention
The invention relates to a process for preparing bis(amidocarboxylic acids) which are key intermediates in the synthesis of bis(amidoperoxycarboxylic acid) bleaches.
2. The Related Art
Peroxyacids have long been known for their excellent fabric bleaching activity. More recently, amido peroxycarboxylic acids have been identified as particularly desirable because of their good stability in detergent compositions.
U.S. Pat. No. 4,634,551 (Burns et al) and U.S. Pat. No. 4,686,063 (Burns) describe peroxyacids having polar amide links along a hydrophobic backbone. All of the reported substances are monoperoxycarboxylic acids. U.S. Pat. No. 5,061,807 (Gethoffer et al) and U.S. Pat. No. 5,132,431 (Fuchs et al) describe a series of imido peroxyacids, chief among which is N-phthaloylaminoperoxycaproic acid (PAP). See also the related technology in EP 0 347 724 (Ausimont).
Bis(amidoperoxycarboxylic acids) have been disclosed in WO 90/14336 (Interox) which especially describes N,N'-terephthaloyl-di(6-aminoperoxycaproic acid), known as TPCAP. The exceptional stability of TPCAP, and related compounds, has occasioned the need for an improved synthesis. A necessary link in this synthesis is a route to the intermediate N,N'-terephthaloyl-di(6-aminocaproic acid) known as TOCAP.
The literature has described various methods for preparation of TOCAP and related compounds. German Patent 949,568 (Kruckenberg) discloses the reaction of caprolactam with various acyl halides including adipoyl dichloride in the presence of sodium hydroxide. Once sodium 6-aminocaproate has formed, the reactor is charged with a first portion acyl halide, sodium hydroxide and then a final portion acyl halide. A related method is reported by Zinner et al in J. Prakt. Chem. 17, 147-153 (1962). The procedure requires the addition of all the sodium hydroxide to be charged to the reaction vessel at the beginning of the synthesis. The reported yield is 70% of theory.
The problem with the aforementioned synthetic routes is that the yields are insufficiently high for commercial purposes. Secondly, these syntheses result in substantial amounts of undesirable by-products, especially the monoamide addition by-product. These by-products can lead to thermal instability and impact sensitivity in any eventual peracid formed therefrom.
A recent co-pending U.S. patent application Ser. No. 08/152,041, filed Nov. 12, 1993 describes a substantially improved method for obtaining TOCAP through the acid chloride route. Therein, an acyl halide is reacted with an amino carboxylate. Condensation is performed in water with sodium hydroxide as catalyst. Excellent yields and minimization of undesirable by-products are achieved by controlling pH between 10 and 14 during the condensation reaction.
Unfortunately no matter how efficient the acyl halide route, there remain certain inherent flaws in this synthetic strategy. Acyl halides are expensive reagents. These materials are not readily commercially available. More economical reagents are required. Since condensation routes using acid chlorides generate a chloride waste stream, there are environmental problems requiring extra engineering and waste disposal. Perhaps the most significant drawback to this process is the generation of chloride ion. Even small amounts of chloride ion will, under peroxidation, convert to hypochlorite, the latter interfering in conversion of TOCAP to TPCAP.
Accordingly, it is an object of the present invention to provide an improved synthesis of bis(amidocarboxylic acids).
Another object of the present invention is to provide a route to bis(amidocarboxylic acids) that achieves high yields.
A further object of the present invention is to provide a route to bis(amidocarboxylic acid) in which undesirable by-products are minimized.
A still further object of the present invention is to provide a route to bis(amidocarboxylic acid) through an environmentally friendly procedure wherein product cleanly and with minimal workup separates from the reaction medium.
Yet a further object of the present invention is to provide a route to bis(amidocarboxylic acid) which avoids contamination by chloride ion.
Still another object of the present invention is to provide a route to bis(amidocarboxylic acid) wherein the amino carboxylate reagent is prepared in a procedure that minimizes water content and need not be isolated from its solvent prior to further reaction.
Yet another object of the present invention is to provide a bis(amidocarboxylic acid) through a procedure that maximizes crystal size of recovered product.
These and other objects of the present invention will become more readily apparent through consideration of the following summary, detailed description and examples.